A majority of modern motor vehicles employ internal combustion engines for propulsion. Additionally, in search of reduced exhaust emissions, as well as for improved fuel efficiency, an internal combustion engine may be combined with one or more electric motor-generators to form a hybrid powertrain. A vehicle employing such a powertrain is generally termed a hybrid.
Cabin warm-up in motor vehicles is typically accomplished via electric heaters and/or via heat exchangers. Typically, the subject heat exchangers are coolant-to-air type, with the engine coolant being used to transfer heat energy to the air that is forced into the vehicle cabin. In certain situations when the vehicle cabin is required to be warmed up, the operation of the engine may be at odds with the desire to shut the engine off for improved vehicle efficiency.